Our objectives are to develop more complete descriptions of the mechanical interactions among the respiratory muscles during normal neural activation and, in the presence of chemical and mechanical stress, when compensatory mechanisms are called into play. Two closely related groups of experiments will be directed toward these major objectives. The first will focus largely on mechanical interactions of respiratory muscles in normal man. Technical aspects and analysis of data will be closely similar in all projects, based upon measurements of the thoracoabdominal dimensions, respiratory pressures and volumes, electrical activity of respiratory muscles, and respiratory gas composition using standard techniques. Project one will extend my earlier analysis of mechanical interaction between the diaphragm and rib cage (limited to normal, upright subjects). Initial observations in the supine posture show substantial differences, and the proposed project will compare mechanical and electromyographic (EMG) relationships between rib cage, diaphragm, and abdomen in upright, supine, and prone postures. Project two will develop a comprehensive analysis of respiratory muscle EMG characteristics during voluntary contraction in normal man, including the effect of strength of contraction and chest wall geometry. Initial descriptive studies will be followed by studies directed at analysis of the neuromuscular basis of fatigue. Project three will develop a mechanical model of abdominothoracic musculature, incorporating the theory of mechanical interaction between diaphragm and rib cage.